1. Field of the Invention
The field of the invention relates to microelectromechanical systems (MEMS). More specifically, the invention relates to voltage regulators for MEMS devices having a display with periods of low current consumption. One particular application can be found in MEMS display devices. The invention also relates to optical MEMS devices, in general, and bi-stable displays in particular.
2. Description of the Related Technology
Microelectromechanical systems (MEMS) include micro mechanical elements, actuators, and electronics. Micromechanical elements may be created using deposition, etching, and or other micromachining processes that etch away parts of substrates and/or deposited material layers or that add layers to form electrical and electromechanical devices. MEMS technology is used, for example, in bi-stable display devices. One type of MEMS bi-stable display device is called an interferometric modulator. As used herein, the term interferometric modulator or interferometric light modulator refers to a device that selectively absorbs and/or reflects light using the principles of optical interference. In certain embodiments, an interferometric modulator may have a pair of conductive plates, one or both of which may be transparent and/or reflective in whole or part and capable of relative motion upon application of an appropriate electrical signal. In this type of device, one plate may be a stationary layer deposited on a substrate and the other plate may be a metallic membrane separated from the stationary layer by an air gap. The position of one plate in relation to another can change the optical interference of light incident on the interferometric modulator.
Because of the bi-stable characteristic of the display, the current load of the display varies greatly. The current load is largest while the display is being driven to change the image, when some or all of the bi-stable elements change states. Between the image update or refresh periods, the current load of the display is near zero. Under extremely low load conditions, the power consumption of conventional power supply regulator circuits dominates the total power consumption of the driver IC. A power supply configured to efficiently source current at a regulated voltage over widely varying current load is needed.